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Rapid extension and active normal faulting in the western extremity of the Corinth Gulf are accompanied by fast coastal uplift. We investigate Pleistocene uplift west of Aigion, by attempting to date remains of marine terraces and sedimentary sequences by calcareous nannoplankton and U-series analyses. Net uplift initiated recently, due to abandonment of an older rift-bounding fault zone and increase in activity on the presently active, coastal fault zone. This change apparently coincides with an abrupt slow down (or, termination) of secondary fault block tilting within the broader hangingwall block of the older zone, indicated by an angular unconformity that dates in the early part of MIS10 (~390-350ka BP, preferably, in the earlier part of this period). Net uplift driven by the coastal zone resulted in the formation of MIS9c (330ka) and younger terraces. The formation of the unconformity and the initiation of net uplift coincide temporally with a ~300-400ka unconformity recognized by recent studies in a wide area offshore Aigion i.e. they could be part of an evolutionary event that affected the entire western part of the Corinth Rift or, a large area therein. Uplift rate estimates at four locations are discussed with reference to the morphotectonic context of differential uplift of secondary fault blocks, and the context of possible increase in uplift rate with time. The most reliable and most useful estimate for uplift rate at the longitude of the studied transect is 1.74-1.85mm/year (time-averaged estimate for the last ~240ka, based on calcareous nannoplankton and sequence-stratigraphic interpretation). © 2009 John Wiley & Sons, Ltd.

International audience

International audience; At the westernmost part of the Corinth Rift (Greece), an area of rapid extension and active normal faulting, geomorphological observations reveal the existence and geometry of an active NW-SE trending coastal fault system, which includes the Aigion fault. We recognize a similar fault pattern on both the coastal range front to the NW of Aigion town and the Holocene fan deltas in front of it. We interpret this as a result of recent migration of faulting to the hanging wall of the fault system. Differences in the geomorphic expression of the constituent faults provide hints on the possible evolution of the fault pattern during this recent migration. A trench excavated across one of the identified coastal fault scarps (on a Holocene fan delta) provides information on the seismic history of the fault system, which includes at least four (possibly six) earthquakes in the past 4000 years. A minimum estimate for the slip rate of the trenched fault is 1.9-2.7 mm/yr. The trench exposed sediments of an uplifted paleolagoon (approximate age 2000 years B.P.), inside which the last two earthquakes formed an underwater monoclinal scarp. Oscillating coastal vertical movements are suggested by the fact that the lagoonal deposits are also uplifted on the trenched fault hanging wall (uplift by offshore faults) and by the abrupt transition from fluvial to lagoonal deposits (subsidence by more landward faults, assuming that extensive coastal sediment failure has not taken place in the specific part of the fan delta, within the time interval of interest). These movements suggest that the proposed migration of activity from the range front faults to those on the fan deltas is probably still ongoing, with activity on both sets of faults.

The 'Île Crémieu', a plateau of Jurassic limestones located in the southern border of the Bresse and at the Jura front, is generally considered as non-deformed. Quaternary ice sheets and drainage have underlined and cleaned out some fracture planes trending NNE and NW-SE that border and crosscut the 'Île Crémieu'. The analysis of seismic profiles reveals NNE-trending normal faults and NW-SE-trending strikeslip faults, crosscutting the basement to Late Miocene layers. Microtectonic fieldwork shows that these faults exist and were activated during the main Cainozoic tectonic events. © 2004 Académie des sciences. Publié par Elsevier SAS. Tous droits réservés.; L'île Crémieu, un plateau de calcaires jurassiques situé au sud de la Bresse et au front du Jura, est généralement considérée comme non déformée. Les glaciers et cours d'eau quaternaires ont souligné et lessivé des plans de fractures NNE et NW–SE, bordant et traversant l'île Crémieu. L'analyse de profils sismiques montre l'existence de failles normales NNE et de décrochements NW–SE, affectant les couches du socle au Miocène supérieur. L'analyse microtectonique sur le terrain confirme l'existence de ces failles et permet de caractériser leurs mécanismes successifs durant les épisodes tectoniques majeurs du Cénozoïque.

This paper describes the development of the CORSSA array (CORinth Soft Soil Array) in the framework of the European project CORSEIS, which takes place in the highly seismic region of Aegion, in the Gulf of Corinth, Greece. An array of surface and down-hole accelerometers and pore pressure transducers is deployed in the hanging wall of the Aegion Fault, an active normal tectonic feature that crosses Aegion city. The scope of this array is to study the physics of wave propagation, the non-linear soil behaviour, liquefaction phenomena and the effects of surface geology on strong ground motion. The surface geology is well constrained by a detailed geotechnical and geophysical survey including dynamic soil tests. Typical recordings and preliminary 1D SH ground response analyses are presented herein, illustrating the importance of the experimental array to study complex site effects including non-linear phenomena in the vicinity of faults and topographic relief. © 2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.

The Atalanti fault bounds to the southwest the Evoikos Gulf, one of the major extensional basins of central Greece. This fault ruptured during the 1894 earthquakes, producing at the surface a complex, ca. 30-km-long rupture. Paleoseismological trenching performed at three sites along this fault provided the first insights on its seismogenic behavior. Unfavorable trench stratigraphy and scarcity of datable material made the identification and characterization of individual paleoearthquakes quite difficult. However, by integrating paleoseismological, geological, historical, and archaeoseismological data, we defined three surface-faulting earthquakes. The most recent event is the 1894 earthquake; the penultimate occurred during the Middle Ages between A.D. 770 and 1160, whereas the third event back occurred in Roman times between 50 B.C. and A.D. 230 and is interpreted to be the Opus earthquake of A.D. 105. These results suggest that 1894-type earthquakes repeat each 660-1120 yr. The average minimum slip per event and vertical slip rates are of the order of 45 cm and 0.4-1.6 mm/yr, respectively. These values are in agreement with other geological estimates and with geodetic measurements. Because of the short time elapsed since the 1894 earthquake, the Atalanti fault does not appear to contain an important seismogenic potential. On the other hand, these results may shed light on the potential of other seismogenic sources threatening the area.

Recent deep boreholes Γ1 (205 m) and AIG 10 (1001 m), performed in the Aigion area, bring new information on syn-rift deposits. MIS1/Holocène (11.8-4.3 ka BP) and Upper Pleistocene are identified in the upper part of the boreholes. Below Holocene deposits, the borehole AIG 10 crossed successively a detrital system with fine intercalations and a thick development of clay. No specific dating was possible on this lower formation, so the age of the local basal syn-rift deposits is discussed. © 2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.

Tectonophysics, v. 387, n. 1-4, p. 1-21, 2004. http://dx.doi.org/10.1016/j.tecto.2004.03.002; International audience; This study deals with the reconstruction of intraplate paleostresses. Calcite twinning inversion provides paleostress directions and differential values, even in poorly outcropping areas. However, existing methods are not well adapted to multi-phase deformation cases, and the calculation of stress values provides unreliable estimates.Modifications were brought to a calcite twinning inverse method and to the processing of results. In a new twin data separation process, the whole set of data is used to calculate each tensor. The variability of yield stress value for twinning with strain hardening is taken into consideration. A first order yield stress-calcite grain size dependence function has been established with a sample showing various grain sizes.This modified method of calcite twinning inversion was applied in the eastern Paris Basin (Lorraine, France). In this platform area, measured fractures are preferentially trending NE–SW and NW–SE at all scales. The Meso-Cenozoic paleostress succession reconstructed with fault slips is complex. Jurassic sedimentation occurred during the Tethys rifting. A mainly strike–slip phase with σ1 successively striking NNW and NNE is attributed to the Tertiary Pyrenean orogenesis, and is followed by WNW extension in the Oligocene. After local ENE compression, WNW compression was probably due to the Alpine Late Miocene collision. The calcite twinning inversion has confirmed these tectonic events and their succession order, and the directions of stress axes were specified. Using grain size- and strain rate-sensitive yield stress values, the differential stresses can be estimated with an uncertainty of few MPa. They range between 20 and 30 MPa, depending on the tectonic event. The Oligocene paleodepths of the sampled calcite, estimated using differential stress values, are structurally sensible.Thus, the original calcite twinning inverse method has been improved. Complex paleostress successions such as in platform areas may be deciphered by combination with fault slip inversion. Even if additional improvement is possible, this calcite twinning inverse method opens new ways to determine stress distributions in tectonic plates.

A 205 m-deep borehole drilled in the Aigion harbour crosses three main sedimentary units: a lower deltaic unit, interbedded with lagoon brackish layers attributed to sea level high stands of marine isotopic stages 5 and 3, an intermediate brackish unit and an upper marine Holocene unit. Environmental conditions of sedimentation are determined by palaeontological studies. 14C ages and correlations with published sea level curves yield preliminary results on subsidence and sedimentation rates. Subsidence rates are close to those inferred from palaeoseismological studies (1.5-3.0 mm yr-1), whereas sedimentation rates are variable (1.5-13.8 mm yr-1). These rates will allow estimating the activity of nearby faults. © 2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS.; Un forage de 205 m situé à Aigion a traversé trois ensembles : un ensemble inférieur deltaı̈que, avec des passées saumâtres attribuables aux pulsations marines des stades isotopiques 5 et 3, un ensemble intermédiaire saumâtre et les dépôts de la transgression holocène. Des datations 14C accompagnent une étude paléontologique des sédiments, précisant les conditions de dépôt. Ces résultats permettent la comparaison avec les courbes de variation du niveau marin connues sur cette période. L'évolution des taux de subsidence (1,5–), proches de ceux obtenus par la paléosismologie, et des taux de sédimentation (1,5–) permettront d'estimer l'activité des failles voisines.

This article presents the results of new field and aerial photo surveys of the Atalanti fault and of the mesoseismal area of the 20 and 27 April 1894 earthquakes. Coupled with a reanalysis of contemporary reports and previous investigations, these are used to gain a better understanding of the faults responsible for these events and their seismic behavior. The first shock was smaller and probably located inshore or offshore the Malessina peninsula. No resolving field evidence has been found to locate the seismogenic structure responsible for this shock. On the basis of the limited information available, we suggest the Malessina escarpment, a 12-km long, ENE-trending, NW-dipping fault as a possible structure responsible for this event. On the other hand, the second and largest shock is definitely related to the Atalanti fault sensu stricto, a main WNW-trending, N-dipping active fault extending between the Platirema valley (a few km NW of the town of Atalanti) and Larymna. The total length of the rupture recognized in the field is about 32 km, but it can be extended further SE up to 40 km. No evidence for a longer rupture extending some other 20 km to the NW, between the Karagiozis river and Ag. Kostantinos, is found. The complex geometry of the fault with bends and step overs appears to be controlled by preexisting transverse structures. Minimum coseismic vertical throws, measured in the field after more than a century elapsed from the earthquake, are 30-80 cm, thus consistent with contemporary reports indicating 1-m average. Slip rates are not well constrained. The available estimates fall in the range 0.1-0.5 mm/yr confirming the smaller amount of crustal extension taking place in this area with respect to other nearby regions such as the Corinth gulf. No new data are available to define the average recurrence interval typical of the Atalanti fault. However, a reconsideration of the existing information induced us to rule out the possibility that the famous 426 B.C. earthquake occurred on the Atalanti fault. On the basis of the extent and size of the rupture recognized in the field, a M 6.8 is estimated for the second and largest shock.